title: A robust assay for dexamethasone in plasma using a heterologous 125I radioligand and a magnetizable solid-phase antiserum.
abstract: An assay using an antiserum raised against a dexamethasone 21-hemisuccinate conjugate and the heterologous radioligand dexamethasone 21-(carboxymethyl) ether was developed, validated, and used to study the pharmacokinetics of this steroid for 12 h following administration to patients with congenital adrenal hyperplasia. Coupling the antiserum to magnetizable cellulose allowed rapid separation of bound/free steroid. A C-21 rather than a C-3 antiserum was used to minimize interference with a main metabolite, 6 beta-hydroxydexamethasone. Close correspondence of assay (0.35 nmol/L) and curve (0.25 nmol/L) sensitivities suggests that interference by matrix effects is minimal. This was confirmed by good agreement in data from the in-house assay and that of a reference procedure. Good precision was demonstrated by the precision profile and Shewhart chart quality control data. The latter also demonstrated the assay was robust and reliable in routine practice.
authors.affiliation: Tenovus Institute for Cancer Research, University of Wales College of Medicine, Heath Park, Cardiff, UK.
authors.forename: N J
authors.initials: NJ
authors.lastname: Cook
authors.forename: G F
authors.initials: GF
authors.lastname: Read
authors.forename: C
authors.initials: C
authors.lastname: Lejeune-Lenain
authors.forename: D
authors.initials: D
authors.lastname: Riad-Fahmy
mesh_terms: D000293:Adolescent; D000312:Adrenal Hyperplasia, Congenital / Q000097:blood*; D000328:Adult; D003907:Dexamethasone / Q000097:blood* / Q000493:pharmacokinetics; D006801:Humans; D007106:Immune Sera; D007457:Iodine Radioisotopes; D008280:Magnetics; D011863:Radioimmunoassay; D011869:Radioligand Assay
chemical_list: D007106:Immune Sera; D007457:Iodine Radioisotopes; D003907:Dexamethasone